WEAVE is a new wide-field multi-object spectroscopy (MOS) facility proposed for the prime focus of the 4.2m William Herschel Telescope. The facility comprises a new 2-degree field-of-view Prime Focus Corrector (PFC) with a 1000-multiplex fibre positioner, a small number of individually deployable integral field units, and a large single integral field unit (IFU). The IFUs and the MOS fibres can be used to feed a dual-beam spectrograph that will provide full coverage of the majority of the visible spectrum in a single exposure at a spectral resolution of ~5000 or modest wavelength coverage in both arms at a resolution ~20000. In order to compensate the field rotation, the Prime Focus Rotator (PFR) is assembled in between the WEAVE Fiber Positioner (system that positions the fibers in the focal plane) and with the Central Can (contains the Prime Focus corrector optics) on the William Herschel Telescope (WHT). The Prime Focus Rotator must provide a rotation degree of freedom for the Fibre Positioner with a high bending stiffness (causing a deflection smaller than 0.008° between interface flanges) adding the minimum mass possible to the system (less than 700kg). This is easily identified as the main design driver to be considered. The Prime Focus Rotator positions the Fibre Positioner to an accuracy of 5 arcsec when tracking and guides all the fibres and other power and control lines through a cable wrap, for which the available space is limited. IDOM proposal to comply with these coupled requirements consists of an optimized structural system with a slightly preloaded cross roller bearing providing the highest possible stiffness to weight ratio. The rotation is driven by means of a direct drive motor powered by a servo drive. For the Cable Wrap, a compact design based on a concept previously developed by IDOM for the Folded Cassegrain Sets the GTC was proposed.
The Gran Telescopio Canarias (GTC) has been recently received two Folded Cassegrain Sets (FC-Sets) composed of an
instrument rotator and the corresponding Acquisition and Guiding (AG) optomechanics. IDOM has been the responsible
for the design, manufacturing, assembly and commissioning of the two units of FC-Sets.
The design combines a compact layout of the mechanical system, enhanced by an innovative cable wrap design,
resulting in a smooth and precise movement, whilst guaranteeing good access to important components and maximizing
the maintainability.
The custom design of the cable wrap as an evolution of the rolling loop type eliminates the need for a cable chain static
housing, minimizing weight and impact on the telescope tube. The AG Mechanics provides the required pointing and
focusing capabilities in a compact configuration.
In January 2010, IDOM is awarded the design and procurement of the two FC-Sets. The final design is approved by
GRANTECAN and the fabrication process starts in Nov 2011. The assembly and commissioning of both units are
completed in April 2011. Once the Factory Acceptance Tests finishes in Dec 2011, all the elements are delivered to the
Observatorio del Roque de los Muchachos (ORM). The Site Acceptance Tests are completed in Feb 2012.
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